The present invention relates generally to an automatic air deflation regulator for use in a blood pressure measuring instrument and, more particularly, to such a regulator which includes a deformable diaphragm having an aperture adapted to increase and decrease in size as a function of the air pressure applied against the diaphragm.
In conventional sphygmomanometer blood pressure instruments, an inflatable cuff is affixed around the extremity of an individual whose blood pressure is to be measured. The cuff is inflated sufficiently to constrict the flow of arterial blood passing through the extremity and then the pressure in the cuff is decreased at a controlled and known rate of deflation until such time as the Korotkoff sound is first heard through a stethoscope or other monitoring device. Deflation continues until the Korotkoff sound ceases. The pressure at the commencement of the sound is noted and recorded as the systolic pressure and at the time it stops as the diastolic pressure.
As it is of utmost importance to maintain a constant rate of deflation, so that the pressure decreases linearly with time, deflation in such instruments is normally controlled by a valve through which air is released at a constant rate. As can readily be appreciated, when the valve has a fixed orifice, air will escape at higher pressures much more rapidly than at lower pressures and this results in a decreasing rate of deflation. This can and does result in inaccurate blood pressure readings. To compensate for this, most blood pressure measuring instruments rely on a manually adjustable release valve which permits constant adjustment of the size of the orifice to accommodate for a decrease in air pressure to maintain this fixed or constant deflation rate. Such manually adjustable valves, however, require operation by physicians, nurses or other trained technicians since a degree of skill is required in order to properly adjust the valve to achieve a constant deflation rate.
With the increased public realization of the importance of monitoring one's blood pressure, there has been a growing demand for such instruments which can be used by an individual in measuring his or her own blood pressure. Since most individuals are not trained and therefore may not possess the skill required to properly adjust the control valves to achieve the constant deflation required to insure accurate and reproduceable readings, two approaches have been taken. Certain manufacturers have provided instruments with a fixed orifice valve. The disadvantages of such a valve have been discussed--they do not provide accurate readings because of their inherent non-constant deflation rate. Other manufacturers have tried semi-automatic valves which attempt to compensate for the decreasing air pressure in order to provide a constant deflation rate. An example of one such valve is described in U.S. Pat. No. 3,504,663 which issued to W. C. Edwards on Apr. 7, 1970. Semi-automatic valves of this type, however, still require a certain amount of adjustment to effect constant deflation and, if improperly adjusted, will not achieve the requisite constant deflation rate. Moreover, such valves are easily clogged by impurities in the air passing through them.
Against the foregoing background, it is a primary objective of the present invention to provide an air deflation regulator or valve for use in an instrument for measuring blood pressure which is capable of providing a constant rate of deflation.
It is still another object of the present invention to provide such an air deflation valve which does not require manual adjustment to compensate for air pressure changes.
It is still another object of the present invention to provide such an air deflation valve which can be easily manufactured.